Method for producing grating images

ABSTRACT

The invention relates to a method for producing a grating image, which has at least one grating field recognizable with the naked eye, in which are disposed grating elements, which are produced by a writing apparatus. In a first procedure step at least one grating element is determined, which completely lies within one working field. Then a sequence of working fields is defined, in which the grating elements are to be produced by the writing apparatus. Finally, the working fields are moved to by a relative movement of a carrier, on which is located a substrate to be inscribed, and the writing apparatus, and the grating elements are written into the substrate with the writing apparatus within the respective working fields.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a National Phase of International Application SerialNo. PCT/EP03/06082, filed Jun. 10, 2003.

FIELD OF THE INVENTION

The invention relates to a method for producing a grating image by meansof a writing apparatus, which has at least one grating fieldrecognizable with the naked eye, in which are disposed grating elements.The invention further relates to an apparatus for preparing and carryingout this method as well as a grating image and a security document withsuch a grating image.

BACKGROUND OF THE INVENTION

Optically variable elements, such as holograms or diffraction gratingimages, due to their optical properties varying with the viewing angleare frequently used as protection from forgery or copy for documents ofvalue, such as credit cards, bank notes or the like, but also forproduct securing on any product packagings. For the mass production ofsuch security elements, usually, so-called “master structures” areproduced, which have the respective phase information about theoptically variable element in the form of a spatial relief structure.This, typically, is a glass substrate with a photoresist coating, inwhich the diffraction structure is preserved in the form of peaks andvalleys. Starting out from this master structure, by duplicating andmolding the relief structure embossing tools of any desired form areproduced, with the help of which the diffraction structures reproducedby the relief structure can be transferred in large quantities tosuitable substrates.

The master structure can represent the complete diffraction structure ofa real hologram, or of a grating image composed of different diffractiongratings. The diffraction gratings differ from each other regarding thegrating constant and/or the azimuth angle and/or the profile structureof the grating lines as well as the contour or the outline of the imagearea covered with the respective diffraction grating.

The grating constant corresponds to the distance between the gratinglines and is of essential importance for the colour of the image area inthe grating image recognizable when viewed from a certain viewing angle.The azimuth angle describes the inclination of the grating linesconcerning a reference direction and is responsible for the visibilityof these image fields viewed from certain viewing directions. The lineprofile generally is responsible for the intensity and plays aparticular role in grating images of zero order. On the basis of thistechnique, therefore, optically variable images, e.g. moving images oralso plastically appearing images, can be produced.

The individual diffraction gratings can be produced eitherholographically or by means of electron beam lithography. Whenholographically recording the diffraction gratings, in an appropriatesubstrate light beams consisting of spatially expanding, uniform wavefields are overlapped. For this purpose, usually, laser radiation isused. With electron beam lithography the diffracting grating lines areexposed directly to an appropriate substrate, the exposure operationfrequently also being referred to as writing operation. For this methodin general a glass plate is used as a substrate, which is coated with alayer sensitive to the respective particle radiation or light radiation(“photoresist”). When exposing, substrate and electron beam can be movedrelative to each other. Here it is possible, to hold the substratemotionless and to electromagnetically deflect the electron beam. Thedeflection range of the electron beam lies within a range of a fewtenths of a millimeter. In case of large-scale deflections, so-called“lens errors” of electron optics will disturb, that are noticeable alsoin the finished diffraction grating. Alternatively, the substrate can bemoved by means of an x-y-table, while the electron beam is heldmotionless. For this purpose, however, a high-precision guiding of thetable is required.

As to be able to produce grating images of the above-mentioned kind withthe help of the electron beam lithography, the entire grating image isdivided into a multitude of small fields of an edge length of up to sometenths of a millimeter. I.e. the grating image independent of thedepicted motif is divided into individual “screen elements”, which bymeans of the electron beam are inscribed with grating lines. Here thegrating lines are written into the individual small fields via thedeflection of the electron beam, while the movement from field to fieldis effected by shifting the table. In this way large surfaces can beinscribed. This kind of electron beam exposure in general is referred toas “stitching mode”. This proceeding, however, has the disadvantage,that the image is composed of many pieces of small surfaces, which uponcloser viewing are visually recognizable, coarsen the image, and lead tocolour errors. In the case of larger image surfaces, such as e.g. lines,which when viewed from one viewing angle are to show a uniform colour,the surface is not provided with an appropriate, uniform diffractiongrating. Instead this diffraction grating is made up of many smallelements. Due to the tolerances when putting together the small surfaceelements, the grating lines extending across the image surface havekinks or gaps, which leads to visible errors.

In the “CPC mode” (Continuous Path Control, product of the company LeicaMicrosystems Ltd.), however, the electron beam is mounted stationary,while the table is moved according to the structures to be exposed. Butthis mode is less suitable for the production of finely structuredgrating images, such as for example guilloche images, or images ormicrowriting divided into fine lines, because these finely structuredimages have a predominant number of short grating lines. For that reasonfor each grating image a number of stop and start operations of thetable has to be effected which reaches the millions. This represents aload for the table mechanism and consumes very much time.

SUMMARY OF THE INVENTION

The invention therefore is based on the problem of creating a methodwhich enables the production of finely structured grating images withthe help of electron beam lithography, and which thereby avoids theaforementioned disadvantages.

The problem is solved by the features disclosed herein.

The invention is based on the finding, that as to avoid optical errorsin grating images, the grating elements producing the optically variableeffect and preferably designed as grating lines, have to be producedcontinuously in one procedure step. Therefore, according to theinventive method only those grating lines are exposed according to thismode, which along their entire length lie within the reach of theelectromagnetic deflection of the electron beam. As to be able tocompose grating images in this way, working fields are defined, towardswhich the table can be moved. Within the individual working fields thegrating lines are exposed along their entire length by deflecting theelectron beam into an appropriate substrate.

According to the inventive method in a first step those grating elementsare determined, the starting points and end points of which (andoptionally intermediate points as well) are lying within the motion areaof the writing apparatus. Then the working fields are defined, in whichthe writing apparatus is moved relative to a carrier, on which asubstrate to be inscribed is located. Finally, the motion path of thecarrier is defined, so as to be able to move the carrier towards theworking fields one after the other and produce the grating elementslying in the respective working field.

The determination of the grating elements preferably is effected withthe help of a data record, which contains information about startingpoints and end points and optionally also intermediate points of thegrating elements forming the grating field, in the form of positioncoordinates.

Within the framework of this invention, grating image preferably meansan image motif recognizable with the naked eye or an alphanumericinformation with diffractive or reflecting effects. Alphanumericinformation also includes a microwriting. The grating image has at leastone grating field recognizable with the naked eye, which can be of anyoutline contour, in which a grating pattern consisting of gratingelements of any form is disposed. Preferably, these grating elementsconsist of grating lines, which can be straight, curved or of any otherdesign.

The diffractive grating images preferably are composed of differentdiffraction gratings. With the inventive method any complicateddiffraction structures up to computer-generated holograms can beproduced.

The inventive method preferably is suitable for producing finelystructured grating images or grating images, which have grating fields,the length and/or width of which lies within a range of 5 μm to 500 μmand preferably amounts to 20 μm to 100 μm.

The grating fields in the case of diffractive grating images areprovided with grating elements, preferably grating lines, with a gratingconstant of about 0.1 to 10 μm, preferably 0.5 to 2 μm.

As a writing apparatus the inventive method preferably uses a particlebeam, in particular an electron beam, because therewith resolutions upto the nanometer range are possible. If grating images are to beproduced, which do not require such a high resolution, for examplegrating images which are based only on reflecting effects, also otherlithography instruments are possible so as to produce the gratingelements in an appropriate substrate. This can be, for example, afocussing UV laser or a precision milling apparatus. For the millingoperation preferably metal plates are used as a substrate. The term“photoresist” within the framework of this invention comprises anysubstrate, into which information in the form of a relief structure canbe incorporated.

The inventive principle of dividing the writing operation into ahigh-precision only-transport operation and a high-precision moving andwriting operation, which is optimized regarding the writing apparatusused, here again can be advantageously applied.

According to a first embodiment, for example, the working fields can bemoved to via a table, which is adapted to be controlled via ahigh-precision mechanism, such as a high-precision spindle. With thistechnique longer distances can be covered relatively fast and veryprecise. For the actual writing operation on the table can be disposed afurther smaller table, which is moved, for example, in a piezoelectricfashion. Alternatively, the small table can be moved by other means,e.g. via magnetostriction. In such a way short distances in themicrometer range can be covered in a fast and exact fashion. I.e.,during the writing operation the substrate to be inscribed is movedrelatively to the stationary writing apparatus by means of thepiezoelectric table, until all elements of the entire motif, accessiblewith the piezoelectric table, are written. Then both the substrate andthe piezoelectric table with the help of the mechanically movable tableare transported to the next working field, in the area of which thesubstrate again is inscribed. This proceeding is suitable preferably formilling apparatuses, but can be used with all other mentioned writingapparatuses. In case an electron beam is used, alternatively it isexpedient, as already mentioned above, to move to the working fields viaa movement of the table, while the grating elements lying in the workingfield are produced by electromagnetic deflection of the electron beam.

For illustrating the inventive method one starts out from a gratingimage, which consists of merely one straight, linear grating field witha width of the above-mentioned range between 0.02 and 0.2 millimeter.The line can have any length. The grating elements of the linear gratingfield are straight grating lines, which extend across the width of thegrating field and thus have a length, which corresponds to the width ofthe grating field. This grating image is to be exposed to a suitablephotoresist with the help of an electron beam. The photoresist islocated on a substrate, preferably a glass plate, which is disposed onan x-y-table mounted to be movable.

For producing this grating image a data record is provided, whichcontains information about the starting points and end points of thegrating lines. This data record, for example, can date from the draftphase of the grating image, in particular when the design of the gratingimage was created in a computer-aided fashion with the help of specialprograms. With the help of these data it is determined, which of thegrating lines lie within the electromagnetic deflection area of theelectron beam. Since the starting points and end points of all gratinglines lie in the area, which can be reached via an electromagneticdeflection of the electron beam, all grating lines can be writtencontinuously without interruption along their entire length. Finally amotion path for the table is determined, on which the photoresist islocated. Having determined all necessary data required for the controlof the individual apparatuses, the first working field is moved to bymoving the table. Within this working field the grating lines areproduced by deflecting the electron beam. The individual grating linesare produced by continuously deflecting the electron beam and do nothave any interruptions or undesired kinks. Having written all gratinglines lying within the area of the first working field, the table ismoved again and the next working field is brought in a position to beexposed. This operation is repeated as long as the entire linear gratingfield is exposed to the photoresist.

The inventive method has the advantage that the individual gratingelements are uniform within themselves in as large as possible areas,and within these areas are not composed of several partial segments.Moreover, by dividing the grating field into working areas the number oftime-intensive stop and start operations of the table are reduced to aminimum.

When the grating fields are to have complicated outline contours, suchas e.g. guilloche lines, it can occur, that the grating elements havestarting points and end points, which lie outside the deflection area ofthe writing apparatus. Such too large grating elements can either beproduced by moving only the substrate while the writing apparatusremains stationary, or by dividing the grating elements into smallerpieces accessible for the writing apparatus, which are put together.

The inventive apparatus for carrying out the inventive method comprisesa transport apparatus, with which the writing apparatus and thesubstrate can be moved relative to each other along a longer distance, amotion apparatus, with which the writing apparatus and the substrate canbe moved relative to each other during the actual writing operation, aswell as apparatuses for controlling the above-mentioned. The motionapparatus can be, for example, the already mentioned piezoelectric tableor an apparatus for deflecting a particle beam or light beam. The motionapparatus enables a fast and precise relative of substrate and writingapparatus in the micrometer range.

In the event of an exposure by electron beam, the apparatus preferablyhas a table mounted to be movable and used only for the transportoperation, as well as an electromagnetic apparatus for deflecting theelectron beam during the writing operation. Additionally, the inventiveapparatus can also contain a processing unit, in which theabove-described motion sequences of the writing apparatus and thecarrier are calculated.

As to have not to spend too much time with calculations during thewriting operation, the preparation and the decision, how the gratingimage in detail is composed, or the calculation of the control data forthe writing apparatus and the carrier preferably take place in acomputer simulation before the actual writing operation. In this phaseis decided, which grating elements lie within the deflection area of thewriting apparatus, how the working fields have to be designed, whichgrating elements lie in which working field, how the carrier has to bemoved so as to be able to move to all working fields in an economicalfashion, whether, and if so, which grating elements are to be producedaccording to a different method.

The inventive method of course can also be used for grating images,which have both finely structured grating image parts and large-surfacegrating image parts. In this case while preparing the writing operationit is determined, which parts of the grating image are to be producedwith the inventive method and which parts are to be produced accordingto a different method.

The writing paths within the working fields can be designed in differentfashions. For example, the writing apparatus can be guided along ameandering or a zigzag path. In the event an electron beam or a laser isused, the meandering guidance has the advantage that the beam does nothave to be turned off along the short connecting sections. In the caseof a zigzag-shaped writing path the beam is turned off while returning,or the retreats are covered so fast, that a relevant exposure does nottake place.

According to an alternative method variant in each working field onlyone line or one grating element is written. I.e., the writing apparatusproduces one grating element at a time, which lies in its working area.At the same time or while retreating the carrier step-by-step orcontinuously is moved from grating element to grating element. Theindividual grating elements can be straight or bent in any fashion. Inthe simplest case the grating elements succeeding each other have anidentical form. But when the writing apparatus is appropriatelyprogrammed any grating elements can be produced.

The substrate produced according to the inventive method after apossible developing step forms a master structure, which can betransferred to any embossing tool. So as to produce these embossingtools, for example, the relief structure of the grating image isrendered electrically conductive, e.g. by spraying on a metal layer, andthen is galvanically molded into a nickel foil. Starting out from thisnickel foil further nickel foils are molded, which, for example, areused for embossing a large number of copies into a thermoplastic plasticplate, e.g. acrylic glass. This plastic plate, too, is galvanicallymolded and the molded metal foil is used as an embossing mold for amultitude of copies of the original grating image. For this purpose themetal foil preferably is welded to form a cylindrical embossing mold andis mounted to a mounting cylinder.

With these embossing tools any layers, such as for example athermoplastic layer or a lacquer layer, in particular a UV curablelacquer layer, can be embossed. The embossable layer is preferablylocated on a carrier material, such as a plastic foil. Depending on theintended use the plastic foil can have additional layers or securityfeatures. Thus the plastic foil can be used as a security thread or asecurity label. Alternatively, the plastic foil can be designed as atransfer material, such as for example in the form of a hot stampingfoil, which serves for the transfer of individual security elements tothe objects to be secured.

The grating images preferably are used for protecting documents ofvalue, such as bank notes, ID cards, passports, and the like. Of coursethey can be also employed for other goods to be secured, such as CDs,books, bottles etc.

According to the invention it is not necessarily required to compose theentire grating image out of grating fields. In fact only parts of awhole image can be realized in the form of grating fields, in particularinventive grating fields, while other image parts are designed with thehelp of other methods, such as for example holographic gratings, realholograms or prints.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the invention are explained with reference to thefigures.

FIG. 1 shows a design, which according to the inventive method isrealized in a grating image,

FIG. 2 shows a highly magnified detail of the inventive grating imageaccording to FIG. 1,

FIGS. 3 a-3 c show the production of a grating field according to theinventive method,

FIG. 4 shows a grating image produced according to prior art,

FIG. 5 shows the production of a grating field with long gratingelements,

FIGS. 6 a-6 d show variants for writing paths within the working fields,

FIGS. 7 a-7 c show a variant of the inventive method,

FIGS. 8 a-8 c show a further variant of the inventive method,

FIG. 9 shows a further variant of the inventive method.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 is shown an inventive grating image 1. The shown example is afinely structured grating image 1, which is composed of guilloche lines2. In this guilloche image 1 the individual guilloche lines 2 arerepresented by different diffraction structures, in particulardiffraction gratings. The diffraction gratings can differ from eachother with respect to their grating constants and/or the azimuth angle,so that when viewed from a certain viewing angle only a part of theguilloche lines 2 can be recognized and the visible guilloche lines 2show different colours. When changing the viewing angle other guillochelines 2 become visible and the colours of the individual guilloche lines2 change. The diffraction gratings can also be designed in such a waythat all guilloche lines 2 are visible from all viewing angles andmerely differ with respect to their colours. In this case, when changingthe viewing angle only an interplay of colours occurs.

In FIG. 2 the detail a is shown highly magnified, so that the individualdiffraction grating lines 5, 7 are visible. The shown guilloche lineshere constitute the inventive grating fields 4, 6, in each of which aredisposed grating elements 5, 7. As already mentioned above, the gratingelements 5, 7 in the present example are formed straight and extendacross the entire width b of the grating fields 4, 6. The form of thegrating fields 4, 6 is determined by the picture motif 1 alone. Widthand length of the grating fields 4, 6 are determined by the motif. Inthe present example of a guilloche line the width preferably lies withina range of 0.02 to 0.2 millimeter. The grating fields 4, 6 here areproduced according to the inventive method. The inventive method isexplained in the following with the help of the grating field 4.

For the production of the grating field 4 in a first step a data recordis provided, which contains information about the form and position ofthe grating elements 5, which preferably exist in the form ofcoordinates in a certain coordinate system. In case the grating linesare straight, the coordinates of the starting points and end points ofthe individual grating elements 5 will be sufficient. This isschematically outlined in FIG. 3 a. Each of the grating lines 5 has astarting point A and an end point B, the coordinates of which are storedin a defined x-y-level in the data record. From the starting points andend points indirectly results the length L of each grating line 5 aswell as the distance of the individual grating lines 5 to each other. Inthe shown example the distance d is constant for all grating lines 5 ofthe grating field 4. However, the distance can vary in any way, alsoalong a grating line which is not disposed in parallel to the nextgrating line, or when the grating lines are designed, for example,wave-shaped.

If the grating lines are not straight, the data record will contain thecoordinates of many intermediate points lying close to each other, whichdescribe the form of the grating elements as a polygonal curve.Alternatively, the form of the grating elements can be described as aBezier curve, in which the coordinates of merely a few intermediatepoints and additionally a tangential direction with respect to thefurther path of the curve are stored.

The coordinates of a grating element, therefore, can only consist of thecoordinates of the starting point and end point of the grating element,or of the coordinates of a certain number of intermediate points andoptionally can comprise information on direction.

With the help of the coordinates of the individual grating elements 5 tobe produced it is determined, which of the grating elements can becontinuously written by deflection of an electron beam. A window of thesize of the working field is defined. Starting out from a definedstarting point this coordinate window is put over the coordinates of thegrating elements and determines, which grating elements succeeding eachother completely lie in the area of this coordinate window. Thecoordinates of the grating lines 5, which lie within a coordinatewindow, are now sorted and arranged in such a way, that polygonal curvesA₁B₁, A₂B₂ and A₃B₃ are the result. This procedure step is shown in FIG.3 b.

In FIG. 3 c are shown, in addition to the polygonal curves A₁B₁, A₂B₂,A₃B₃, the working fields 8, 9, 10. When determining the position of theworking field 8, for example, the y-coordinate of the coordinate windowis set on the y-value of the starting point A₁, and the coordinatewindow is adjusted along the x-direction as long as the end point D ofthe first grating element completely lies within the defined coordinatewindow. Then the coordinates of the following grating elements arecompared to the coordinates of the window and checked, whether they liecompletely within the area of the coordinate window. At this stage theposition of the coordinate window can still be optimized. From thiscomparison of the coordinates of the window and those of the gratingelements finally results, that the grating element 100 is the lastgrating element, which completely fits into the coordinate windowbeginning at A₁. The working field 8 ends with the end point B₁ of thegrating element 100.

For determining the working field 9 the coordinate window, due to theinclination of the grating field 4 in y-direction, is set on the endpoint B₂ of the following grating element 101 and again is adjusted aslong as the maximum possible complete number of grating elements islying within the coordinate window. This operation is carried outcomputer-aided and repeated as long as all grating elements areallocated to a working field. As appearing from FIG. 3 c the workingfields 8, 9, 10 can overlap each other.

The size of the working fields 8, 9, 10 here corresponds to the size ofthe electromagnetic deflection area of the electron beam. For exposingthe substrate, at first the table is brought in such a position, thatthe working field 8 comes to lie under the electron beam. The electronbeam is electromagnetically deflected and moved along the polygonalcurve A₁B₁, and the respective grating lines 5 are written. As it willbe explained in still more detail in another passage, here the shortconnecting sections 11 between the grating lines 5 within a polygonalcurve A₁B₁, A₂B₂, A₃B₃ can be exposed too or not. Then the table isshifted in such a way, that the working field 9 comes to lie under theelectron beam. The electron beam covers, by means of electromagneticdeflection, the polygonal curve A₂B₂ and exposes the respective gratinglines 5 to the substrate. The working field 10 and the polygonal curveA₃B₃ are treated analogously. This operation is carried out as long asthe entire grating field 4, in the present case the guilloche line 2,with the help of the electron beam is exposed to the substrate. Theother grating fields of the grating image 1 are treated analogously.

FIG. 4 shows the grating field 4, in the event it is produced accordingto the known stitching mode. The “screen elements” 30 independent of thedepicted motif, in which are disposed partial sections of the gratinglines, are clearly recognizable. Since the screen elements are notadapted to be put together exactly adjoining each other, the mostgrating lines extending across the width of the grating field have gapsand kinks, as recognizable in the marked area c.

FIG. 5 shows a variant of the inventive method, in which a grating field20 is to be written, which, too, has a linear outline contour. Thegrating lines forming the grating field 20 partly consist of gratinglines 12, the coordinates of which are lying in the deflection area ofthe electron beam. Furthermore, the grating field 20 has large gratingelements, the coordinates of which lie outside the deflection area ofthe electron beam. In the shown example these grating elements are alsograting lines 13.

In this case, too, inventive working fields 14, 15, 16, 17, 18 aredefined, in which are disposed the respective, according to the alreadydescribed method, writable polygonal curves A₁,B₁, A₂B₂, A₄B₄, A₅B₅ andA₆B₆. The intermediate area, consisting of the polygonal curve A₃B₃,however, cannot be written according to the inventive method. Havingexposed the working field 15 to the substrate according to the inventivemethod, for a short term another writing mode is used. In the shownexample the polygonal curve A₃B₃, too, is written continuously merely bymoving the table. I.e., the electron beam is not deflected and ismounted stationary, while the table and the substrate to be exposedlocated thereon are moved relative to the electron beam corresponding tothe polygonal curve A₃B₃.

As already mentioned above, those polygonal curves lying in one workingfield can be exposed exactly in this form to the substrate. However,there are further possibilities for designing the writing paths withinthe respective working fields. The different possibilities for guidingthe writing apparatus are described by way of example with the help of apolygonal curve, which is worked through within a working field.

In FIG. 6 a the variant is shown, in which merely the grating lineswithout the connecting sections 11 of the polygonal curve are to beexposed to the substrate. I.e., the electron beam having written thegrating line 21 in the substrate, namely from the starting point A₁ tothe end point B₁, has to cover an “idle way” to the starting point A₂ ofthe next grating line 22. The idle ways on the connecting sections 11are drawn as dashed lines in FIG. 6 a. On this idle way the electronbeam can be turned off or in another fashion be prevented from exposingthe substrate.

Since the short-term turn-off of the electron beam on the connectingsections 11 consumes time and disturbs the course of procedure, theconnecting sections can also be exposed, so that in the substrate indeeda meandering polygonal curve with the starting point A₁ and the endpoint B₁ does exist. This small written edge sections due to theirshortness do not spoil the optical impression of the entire gratingimage.

The connecting sections 11 do not have to be of a straight design, butcan also be rounded, with the help of which the writing speed of theelectron beam can be further increased. This embodiment is shown in FIG.6 c.

The meandering writing paths as shown in FIG. 6 a to 6 c are veryuseful, because they shorten the writing paths, but according to theinvention they are not necessarily required. In FIG. 6 d a differentpossibility is shown as to guide the writing apparatus, in particularthe electron beam, between the individual exposure operations. Here theelectron beam is guided starting from the starting point A₁ of thegrating line 21 to the end point B₁ of the grating line 21 for exposingthe grating line 21 to the substrate. Then the electron beam isdiagonally guided back via the connecting section 23 to the startingpoint A₂ of the grating line 22. On this diagonal connecting distance 23an exposure of the substrate does not take place. Then the grating line22 from the starting point A₂ of the grating line 22 to the end point B₂of the grating line 22 is exposed to the substrate. This operation isrepeated in a kind of zigzag course until all grating lines of theworking field are written. On the dashed drawn connecting line 23 theelectron beam is either turned off or moved so fast, that an exposuredoes not take place.

FIG. 7 a to 7 c show a special embodiment of the inventive method, inwhich in the working area, i.e. in the deflection area of an electronbeam, only one line is written. In FIG. 7 a a respective line 301 withthe starting point A₁ and the end point B₁ is shown. Along this line 301the electron beam moves within its deflection area. The carrier eithermoves step-by-step or continuously with an appropriate speed along themotion path 31. In FIG. 7 b the overlapping of the carrier movement 31with the movement of the electron beam is shown. In the shown detail ofthe process the electron beam has already written the grating lines 301to 309, while being turned off on the retreat between the end point ofthe respective written line and the starting point of the next line.This is indicated by the dashed connecting lines 32. In FIG. 7 c,finally, the completely written grating image 33 is shown, whichconsists of equally long grating lines, which are disposed along themotion path 31.

In FIG. 8 a to 8 c a similar variant of the inventive method is shown,in which the electron beam in its deflection area writes a complicatedgrating line 401 with the starting point A₁ and B₁. Here, too, theelectron beam is turned off on the retreat 42. For clarity's sake thestraight retreat 42 is not drawn into FIG. 8 b. Here merely the gratinglines 401 to 420 written along the motion path 41 are shown. Thecomplete grating line image 43 is shown in FIG. 8 c.

If the electron beam motion after each writing operation or after eachtravelling back is separately programmed, also any other gratingstructures along a motion path of the carrier can be written. Such avariant is schematically shown in FIG. 9. In the shown example the formof the grating lines varies along the motion path 51. The grating line501 is strongly curved. Along the motion path 51 the grating linesgradually become longer and their form more and more approaches the formof a straight line. The grating line 519 is practically straight andsubstantially longer than the grating line 501.

In the event the grating lines do not lie completely in the deflectionarea of the electron beam, they can either be divided into smallerpieces or a different writing mode (e.g. CPC) is applied.

1. Method for producing a grating image, which at least has one grating field with visually recognizable, optically variable properties, in which grating elements are disposed, that are produced by means of a writing apparatus, the method comprising the following steps: a) determining at least one grating element, which completely lies within one working field; b) defining a sequence of working fields, in which the grating elements are to be produced by means of the writing apparatus; c) moving to the working fields by relative movement of a carrier, on which is located a substrate to be inscribed, and the writing apparatus; d) writing the at least one grating element into the substrate with the writing apparatus within the respective working fields.
 2. Method according to claim 1, characterized in that the determination of the grating elements in step a) is effected with the help of a data record, which contains information about form and position of the grating elements forming the grating field.
 3. Method according to claim 1, characterized in that the data record contains the coordinates of the starting points and end points of the grating element.
 4. Method according to claim 3, characterized in that the data record contains the coordinates of several intermediate points.
 5. Method according to claim 1, characterized in that the data record contains the coordinates of Bezier curves, which describe the form of the grating elements.
 6. Method according to claim 1, characterized in that with the help of the coordinates it is determined, which grating elements can be continuously produced in one writing operation.
 7. Method according to claim 1, characterized in that a coordinate window of the size of the working field is defined, and in step b) is put over the coordinates of the grating element.
 8. Method according to claim 7, characterized in that starting out from a defined starting point it is determined, which grating elements succeeding each other completely lie in the area of this coordinate window.
 9. Method according to claim 7, characterized in that the coordinates of the grating elements within a coordinate window are sorted in such a way, that polygonal curves are the result.
 10. Method according to claim 7, characterized in that all working fields are determined with the help of the coordinate window.
 11. Method according to claim 1, characterized in that as a writing apparatus a light beam or a particle beam is used.
 12. Method according to claim 1, characterized in that as a writing apparatus an electron beam is used.
 13. Method according to claim 1, characterized in that the writing in of the grating elements in step d) is effected by deflection, of the writing apparatus.
 14. Method according to claim 1, characterized in that the size of the working fields corresponds to the size of the deflection area of the writing apparatus.
 15. Method according to claim 1, characterized in that when writing in the grating elements in step d) the writing apparatus is mounted stationary and the carrier is moved.
 16. Method according to claim 1, characterized in that as a carrier a movably mounted table is used.
 17. Method according to claim 1, characterized in that the working fields in step c) are moved to by moving the carrier.
 18. Method according to claim 1, characterized in that the grating field has the form of a line.
 19. Method according to claim 1, characterized in that as grating elements grating lines are used.
 20. Method according to claim 1, characterized in that the grating lines at least in certain areas extend across the width of the grating field.
 21. Method according to claim 1, characterized in that the grating lines are formed straight or curved.
 22. Method according to claim 1, characterized in that in at least one working field only one grating element is produced.
 23. Method according to claim 22, characterized in that in each working field only one grating element is produced and the individual positions of the grating elements along a motion path are moved to by a stepwise or continuous movement of the carrier.
 24. Method according to claim 1, characterized in that all grating elements have the same form.
 25. Method according to claim 1, characterized in that the grating elements have different forms.
 26. Method according to claim 1, characterized in that the grating image has large grating elements, the coordinates of which at least partly lie outside the working field, and that these grating elements are produced according to a different method.
 27. Method according to claim 26, characterized in that these large grating elements are produced continuously by shifting the carrier.
 28. Method according to claim 26, characterized in that these large grating elements are divided into processing areas, the size of which corresponds to maximally one working field.
 29. Method according to claim 28, characterized in that the processing areas are moved to successively by shifting the carrier and the parts of the large grating elements lying in the respective processing area are produced.
 30. Method according to claim 1, characterized in that when defining the sequence of the working fields also the processing areas are taken into account.
 31. Method according to claim 1, characterized in that the large grating elements are long grating lines, the coordinates of which lie outside the deflection area of the writing apparatus.
 32. Method according to claim 1, characterized in that the writing paths of the writing apparatus within the respective working fields or processing areas have a meandering or zigzag shape.
 33. Method according to claim 1, characterized in that in a data processing system at first all coordinates necessary for the production of the grating elements are determined, and then the writing apparatus with the help of these coordinates produces the grating elements in the substrate.
 34. Method according to claim 1, characterized in that as a substrate a radiation-sensitive material is used, in which the writing apparatus causes a change of state.
 35. Method according to claim 34, characterized in that as a radiation-sensitive material a photoresist layer is used.
 36. Method according to claim 1, characterized in that onto the substrate provided with the grating elements a metallization is applied, and a metallic molding is galvanically produced therefrom.
 37. Method according to claim 36, characterized in that the molding is used as an embossing tool for embossing a grating image into a layer.
 38. Method according to claim 1, characterized in that the grating image has several grating fields.
 39. Method for defining the coordinates of movement of a writing apparatus and a carrier for producing a grating image, which has at least one grating field recognizable with the naked eye, in which grating elements are disposed, the method comprising the following steps: determining the grating elements, the coordinates of which lie within a predetermined coordinate window; defining a sequence of working fields, in which the writing apparatus is moved relative to a carrier, on which is located a substrate to be inscribed.
 40. Method according to claim 39, characterized in that for determining the coordinates of the grating elements a contour line of the grating field is defined and the contour line is filled with the grating elements.
 41. Method according to claim 40, characterized in that the grating elements are grating lines and as grating coordinates the intersection points the grating lines have with the contour line of the grating field are used.
 42. Method according to claim 39, characterized in that the method is carried out with the help of a data processing system.
 43. Apparatus for defining the coordinates of movement of a writing apparatus and a carrier for producing a grating image, which has at least one grating field recognizable with the naked eye, in which grating elements are disposed, the apparatus having the following devices: a device for determining at least one grating element, which completely lies within one working field; a device for defining a sequence of working fields, in which the grating elements are to be produced by means of the writing apparatus; a device for defining the motion path of at least one of the writing apparatus or the carrier, on which is disposed a substrate to be inscribed, so that the working fields are successively moved to and the grating elements lying in the respective working field can be produced.
 44. Apparatus according to claim 43, characterized in that the apparatus has a device for determining the coordinates of the grating elements.
 45. Apparatus according to claim 43, characterized in that the apparatus is a data processing system.
 46. Grating image, which has at least one grating field recognizable with the naked eye, in which grating elements are disposed, a greater part of the grating elements having a length of less than 0.2 millimeter, preferably 0.05 millimeter, and being continuous.
 47. Grating image according to claim 46, characterized in that the grating elements are grating lines.
 48. Grating image according to claim 46, characterized in that the grating field also has long grating lines with a length of more than 0.02 millimeter.
 49. Grating image according to claim 48, characterized in that the long grating lines are composed of several partial sections.
 50. Grating image according to claim 46, characterized in that the grating image has several grating fields.
 51. Apparatus for carrying out the method according to claim
 1. 52. Grating image produced according to claim
 1. 53. Security element with at least one grating image produced according to claim
 1. 54. Security element with at least one grating image according to claim
 46. 55. Security element according to claim 53, characterized in that the security element is a security thread, a label or a transfer element.
 56. Security paper with at least one grating image produced according to claim
 1. 57. Security paper with at least one grating image according to claim
 46. 58. Security paper with a security element according to claim
 53. 59. Security document with at least one grating image produced according to claim
 1. 60. Security document with at least one grating image according to claim
 46. 61. Security document with a security element according to claim
 53. 62. Security document with a security paper according to claim
 56. 63. Transfer material, with at least one grating image, produced according to claim
 1. 64. Transfer material, with at least one grating image according to claim
 46. 65. Embossing tool with at least one grating image, produced according claim
 1. 66. Embossing tool with at least one grating image according to claim
 46. 67. The method of claim 13 wherein said deflection is by electromagnetic deflection.
 68. The transfer material of claim 63, comprising hot stamping foil.
 69. The transfer material of claim 64, comprising hot stamping foil. 